In recent years, much attention has been paid to a projection type display apparatus (projector) using a plurality of light sources, as projection type video equipment capable of large screen display (refer to, for example, Japanese Patent Laid-Open No. 2000-171901).
The entire disclosure of Japanese Patent Laid-Open No. 2001-171901 is incorporated herein by reference in its entirety.
These projection type display apparatuses (1) light a light modulating element (a transmission or reflection type liquid crystal or a DMD (Digital Micromirror Device) that can change a reflection direction using micromirrors arranged in an array) capable of light modulation, utilizing light radiated by a light source, (2) form an optical image on the light modulating element in accordance with an externally supplied video signal, and (3) use a projection lens to enlarge and project the optical image on a screen, the image being illumination light modulated by the light modulating element.
(A) An important optical characteristic of enlarged projective display on a large screen is the uniformity of brightness within the display screen.
For the uniformity of brightness within a display area, it is important that the light modulating element is irradiated with light generated by a lamp as a luminous flux that has a relatively uniform brightness in a central and peripheral portions of the area. That is, it is important that the brightness of a luminous flux is uniform.
FIGS. 10 and 11 show a conventional lighting apparatus using a plurality of light sources and implementing a projection type display apparatus using a transmission type liquid crystal panel as a light modulating element and a projection lens.
FIG. 10 shows an optical system using lens arrays 122 and 123 in which a plurality of lenses are two-dimensionally arranged, as an optical element called an integrator and enabling uniform lighting. Furthermore, FIG. 11 shows an optical system using a square-pole-like glass rod 125 as an integrator.
Light emitted by lamps 151 and 161 of these lighting apparatuses (see FIGS. 10 and 11) is (1) collected by ellipsoidal mirrors (concave mirrors) 152 and 162, (2) emitted through openings in the ellipsoidal mirrors 152 and 162, and (3) reflected by a triangle-pole-like prism 131 of a synthesis mirror section 130 that reflects a plurality of luminous fluxes in a predetermined direction, the prism 131 having reflective-coated sides.
The flux reflected by the prism 131 has a nonuniform brightness and has a large difference in luminance between the vicinity of the center and the peripheral portion of the luminous flux.
Thus, in order to make uniform the luminance on the area to be lighted, the luminous flux reflected by the prism 131 is split into partial fluxes. Then, the partial fluxes are super imposed on the area to be lighted to improve the uniformity of the illumination light.
If the lens arrays 122 and 123, in which a plurality of lenses are two-dimensionally arranged, are used (see FIG. 10) , a luminous flux incident on a lighting unit section 120 is made almost parallel with the optical axis of the lighting unit section 120 by a relay lens 121. The fluxes are then split into partial fluxes by the lens array 122, in which a plurality of first lenses are two-dimensionally arranged. Then, owing to the lens array 123, which has lenses corresponding to the individual lenses in the lens array 122, the partial fluxes then form images similar to respective lens openings in the lens array 122 and are then superimposed on an area of a light receiving section 110 which is to be lighted.
The luminous flux having nonuniform brightness when entering the lens array 122 is split into the partial fluxes having different luminance distributions. The partial fluxes are then superimposed. In this manner, lighting is achieved which has improved uniformity within the area to be lighted.
If the square-pole-like glass rod 125 is used (see FIG. 11), a luminous flux incident on the lighting unit section 120 enters a facet of the glass rod 125. The light entering the interior of the glass rod 125 is emitted from a facet of the glass rod 125 which is opposite its entry facet while being transmitted through the glass rod 125 or being totally reflected. At this time, the light emitted from the exit facet is totally reflected inside the glass rod 125 a number of times corresponding to the angle at which the light has been incident on the glass rod 125. Accordingly, the partial fluxes are emitted from one opening, the exit facet of the glass rod 125, at different angles. The partial fluxes are superimposed by a relay lens 124 on the area of light receiving section 110 which is to be lighted.
The luminous flux having nonuniform brightness when entering the glass rod 125 is split into the partial fluxes having different luminance distributions. The partial fluxes are then superimposed. In this manner, lighting is achieved which has improved uniformity within the area to be lighted.
Thus, a projection type display apparatus using the lighting apparatus (see FIGS. 10 and 11) can display a video with a highly uniform brightness by enlarging an image formed by a liquid crystal panel (not shown) arranged on a lighted surface as a light modulating element, on a screen (not shown) via a projection lens (not shown)
(B) FIG. 12 shows a lighting apparatus system configured similarly to the above lighting apparatuses and using nine lighting apparatuses 300 to project light from behind a transmission type multiscreen 500 so that the multiscreen 500 can form one integrated video on a screen.
By utilizing the lighting apparatus system (see FIG. 12) that displays one integrated video using the plurality of lighting apparatuses 300, it is possible to display videos of higher resolutions or simultaneously display many pieces of information.
(A) The inventors have found that with an optical system using a plurality of light sources as described above, not all the plural light sources may be simultaneously used and some of the plural light sources may be used in accordance with a user's manual operation.
More specifically, high-pressure mercury lamps that are light sources often used in lighting apparatuses have a lifetime of about 2,000 to 5,000 hours, which is relatively shorter than that of a set, which is about 5 to 10 years. Thus, if no particular requests have been made for the brightness in the display screen or the time remaining before the lamps must be replaced is to be maximized, some of the plural light sources are often used.
Furthermore, if a plurality of light sources are used but trouble occurs such as the sudden breakage of any lamp or a failure to light any lamp, some of the plural light sources are used.
However, in an optical system using a plurality of light sources, the devices are designed so as to provide uniform lighting assuming the usage of all the light sources. In short, with an optical system using a plurality of light sources, the uniformity of the brightness in the display screen may be degraded if not all the plural light sources are used.
(B) The inventors have also found that with a lighting apparatus system that displays one integrated video using a plurality of lighting apparatuses, the brightness may vary in a wavy form within one integrated video as shown in FIG. 13.
More specifically, the 3×3 multiscreen 500 has the brightest part in a central portion of a small screen corresponding to each lighting apparatus and the darkest part in a peripheral portion of the small screen. Accordingly, in one integrated video, (1) the brightness distribution in the direction of a vertical axis is shaped like mountains having three peaks as shown in a graph 601, while (2) the brightness distribution in the direction of a horizontal axis is shaped like mountains having three peaks as shown in a graph 602.
However, such a variation in brightness in a wavy form within one integrated video may result in an esthetically unfavorable impression on many users. In short, a lighting apparatus system that displays one integrated video using a plurality of lighting apparatuses may have a degraded display grade.